Recently, various types of materials have been studied as an electrode material for an energy storage device. Among the materials, lithium titanate is attracting attention for its superior input-output performance when used as an active material.
Patent Document 1 discloses lithium titanate containing Li4/3Ti5/3O4 as a main component, having a main peak intensity of 5 or less in each of anatase-type titanium dioxide, rutile-type titanium dioxide, and Li2TiO3 when the intensity of the main peak for Li4/3Ti5/3O4 determined by X-ray diffraction analysis using Cu target is defined to be 100, and with high crystallinity having a crystallite diameter of 700 Å to 800 Å (70 nm to 80 nm), which is determined from a half-peak width of the peak in 4.83 Å with the Scherrer equation. According to Patent Document 1, high initial charge-discharge capacity is achieved by the peak intensity being as small as 5 or less in lithium titanate components other than Li4Ti5O12 and very high crystallinity having a crystallite diameter of within the range of 70 nm to 80 nm.
Patent Document 2 discloses a lithium-titanium complex oxide containing Li4Ti5O12 as a main component, and when the main peak intensity detected for each phase of Li4Ti5O12, Li2TiO3, and TiO2 in the X-ray diffraction pattern is I1, I2, and I3 respectively, achieving I1/(I1+I2+I3) of 96% or more, and also having a crystallite diameter, which is determined from the half-peak width of the peak in the X-ray diffraction pattern for the (111) plane of Li4Ti5O12 with the Scherrer equation, of 520 Å to 590 Å (52 nm to 59 nm). Patent Document 2 also discloses that a lithium-titanium complex oxide preferably has a ratio of a specific surface area equivalent diameter determined by the BET method to the crystallite diameter, that is a specific surface area equivalent diameter/crystallite diameter, of 4 or less, further preferably, has a specific surface area determined by the BET method of 8 to 12 m2/g and maximum primary particle diameter of 1.5 μm or less. According to Patent Document 2, lithium-titanium complex oxide having a crystallite diameter within the above range can form fine particles while having high crystallinity, and is considered to exhibit high-rate performance while having a high initial capacity of 160 mAh/g for example.